replace constant dicts with namedtuples

[smoors]

this will be a life changing improvement that must get top priority.

example:

from typing import NamedTuple

class DeviceTypes(NamedTuple):
    CPU: str = 'cpu'
    GPU: str = 'gpu'

DEVICE_TYPES = DeviceTypes()

print(DEVICE_TYPES.GPU)  # 'gpu'

advantages:

• really constant, you cannot change the value directly
• you only have to import DEVICE_TYPES, not CPU or GPU
• strings 'CPU' and 'GPU' don't have to be defined anymore
• thus, you cannot mistakenly use the 'CPU' or 'GPU' strings anymore
• easier syntax DEVICE_TYPES.CPU instead of DEVICE_TYPES[CPU]: saves a full character!

for SCALES this is probably not a good idea, as we really want to use the strings themselves, e.g. on the cmd line.

[smoors]

thinking more about the SCALES, maybe it is still useful to have constants for the strings, and it doesn't prevent you from still using the strings directly if you want?

EDIT: scratch that, Python doesn't allow variables that start with a number, like 1_NODE